Study On The Effect Of Contamination On The Performance Of Coated Optics During Storage And Use Process

High energy/high power laser optics which are used in different environment may suffer from different degrees of contamination.The contaminations include organics,particles,etc.These contamination may lead to the degradation of the stability of optics'performance and shorten lifetime of the optical systems.High energy/high power laser optics will always be coated with optical films to maintain its performance.As the weakest link in high energy/high power laser systems,optical coatings are the key factor which will restrict the optical system's performance and lifetime.In this paper,we analyzed the mechanism of formation of contamination on the surface of optics in different environments.We set up environment simulation devices for simulation tests according to the actual use conditions of optics.The effects of organic contamination in vacuum and contamination in clean laboratory environment on the stability of the coatings'performance are investigated respectively.Various types of contaminations that threaten coated optics in high-energy/high-power laser systems are analyzed firstly,including the types of contaminations,the origin of the contaminations,the way contamination propagates,and the process by which coated optics adsorb the contamination.The influence of contamination on the performance of coated optics is also introduced.The mechanism of component damage caused by surface contamination in continuous laser systems and pulsed laser systems is introduced and compared in detail.The essential reason for the damage of the coated optics caused by contamination in the high-power continuous laser system is revealed.In order to investigate the influence of vacuum environment on the performance of the optical coatings,a low-loss highly-reflective?HR?coating sample at 1064nm fabricated by Ion Assisted Deposition is stored in a stainless steel vacuum chamber with pressure less than 10^-5Pa to simulate the contaminating process caused by organic contamination in vacuum.We observed the variation of absorptance and reflectance of the HR sample.We compared the differences in the absorptance of the sample,reflectivity of the sample and surface morphology of the sample before and after wiping.Combining the monitoring results of the mass spectrometer,we try to illustrate the mechanism of performance degradation of 1064nm optical coatings caused by organic contamination in vacuum.The results indicate that a thickness increase of an organic contamination layer on the coating surface human errors during the experimental procedure are major sources for the performance degradation of the HR coating.By wiping the sample with mixed alcohol/ether solution,the optical performance of the sample is recovered totally.It means that contamination does not affect the coating structure and optical constants of the sample.In order to investigate the influence of clean laboratory environment on the performance of the optical coatings,a high-reflective?HR?coating sample is stored in the clean laboratory to simulate the contaminating process caused by contamination in clean laboratory environment.During the process of experiment,we use the particle counter to determine the specific cleanliness value of the clean laboratory,and reflectivity scanning system is also used to measure the reflectivity of the sample regularly.And we can monitor the change of the reflectivity of the sample.Combining with the evolution of 2D-reflectivity-graphics at 1064nm,we investigate the laws of contaminating and performance degradation in clean laboratory environment.The experiment shows that in clean laboratory with M3 cleanliness,the optical performance of coated optics can be maintained for a long time?In this experiment,the reflectivity of the sample can remain unchanged for 72 hours.?.However,long-term personnel activities in the laboratory will aggravate the surface contamination of the sample and ultimately affect the optical performance of the sample.